Redundant array of independent disks (RAID) is a data storage virtualization technology, which combines a plurality of physical disk drives into a single logic unit for the purpose of data redundancy backup and/or performance improvement. With RAID 5 as an example, it may include block-level stripes having distributed check information. Upon failure of a single drive, subsequent reads can be calculated from the distributed parity information such that no data is lost. Meanwhile, a spare disk is to be selected to replace a failed disk. All data on the failed disk is to be rebuilt and written into the spare disk. In conventional RAID, a RAID group (RG) will consume all disk space in the group, which adversely influences effects and costs of failure rebuilding.